Tieline i-Mix G3, Основное руководство по эксплуатации

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Section 22: Connection Setup
T
ieline
T E C H N O L O G Y
Page 208
22.9.1. What’s the difference between MPEG-1, MPEG-2, MPEG-3 &
MPEG-4?
The differences between MPEG 1, 2, 3, and 4 have resulted from
evolutionary advances in audio coding over the past decade or so. Each
subsequent set of MPEG standards has provided greater compression
efficiency and more options for coding not only audio, but video as well.
In the following sections we will give a brief overview of MPEG audio. If you
require more detailed information on MPEG audio it can be sourced from
http://www.chiariglione.org/mpeg/
22.9.1.1. MPEG-1
This was the first set of MPEG standards produced and it has three
operation modes or ‘layers’. These are:
Layer-1: The compression used in Digital Compact Cassettes;
Layer-2 (MP2): The MUSICAM ®
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compression format used in
CDs and Video CDs ; and
Layer-3 (MP3): the MP3 compression format used widely to rip
tracks from CDs for portable digital music players.
MPEG-1 layers can provide single channel, dual channel, stereo and joint
stereo coding and all of these operating modes are supported in
T
ieline
codecs. Each ‘layer’ has improved upon the previous one by performing
better at lower bitrates.
The sampling frequencies available for MPEG-1 include 32kHz, 44.1kHz
and 48kHz.
T
ieline
codecs support 32kHz and 48kHz sampling
frequencies for MPEG-1 algorithms.
MPEG 1 Layer 2 (
MP2)
is included in
T
ieline
codecs.
22.9.1.2. MPEG-2
MPEG-2 standards followed the MPEG-1 standards and were designed to
be the successor to the popular MP3 format. The standards included the
attributes of MPEG-1 as well as:
Backwards compatibility with MPEG-1;
Surround sound 5.1 capability (please note that MP3 surround has
since become available); and
Coding at the lower sampling frequencies (LSF) of 16 kHz, 22.05
kHz and 24kHz using Layer-1, Layer-2 and Layer-3.
Of particular relevance to T
ieline
codec users is the ability to encode at
lower sample frequencies. This enables mono and stereo audio to be
encoded using fewer bits and requiring less connection bandwidth.
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